1. Field of the Invention
The invention relates to shutter glasses and a shutter control method, and particularly relates to shutter glasses and a shutter control method capable of reducing darkness of visual range obtained when seeing space outside a display screen of a display during viewing 3D video.
2. Description of the Related Art
In recent years, 3D video contents in which video can be viewed in a three-dimensional manner attract attention. As a system for viewing 3D video, two types of systems can be cited, which are a glasses system using polarizing filter glasses or shutter glasses, and a naked eye system not using glasses, such as for example, a lenticular system and a parallax barrier system.
FIG. 1 is a view showing perception principle of 3D video according to the system using shutter glasses.
On a display 1, video for a left eye and video for a right eye are alternately displayed in order of, for example, a video for the left eye L1, a video for the right eye R1, a video for the left eye L2, a video for the right eye R2, a video for the left eye L3 and a video for the right eye R3 . . . in time series.
On the other hand, a user who views 3D video wears shutter glasses 2. A timing signal for timing of opening and closing shutters is supplied to the shutter glasses 2. The shutter glasses 2 control open and close of a shutter for a left eye and a shutter for a right eye in accordance with the timing signal. Specifically, the shutter glasses 2 repeat open and close operations of two shutters, which are a shutter open operation for the left eye as well as a shutter open operation for the right eye and a shutter close operation for the left eye and a shutter close operation for the right eye alternately so that they are synchronized with the timing signal. As a result, only video for the right eye is inputted to the right eye of the user and only video for the left eye is inputted to the left eye. Parallax is provided in the video for the left eye and the video for the right eye, and the user can perceive 3D video due to the parallax included in 2D video.
The above system is also called a shutter glasses system or an active stereo system. For transmission/reception of the timing signal, an infrared communication is applied, and a transmitter for an infrared signal is mounted on the display side and a receiver for the infrared signal is mounted on the shutter glasses 2 side.
As it is necessary to display the video for the left eye and the video for the right eye in time series in the shutter glasses system, a high display speed (display rate) is necessary. Accordingly, a CRT (Cathode Ray Tube) display has been used as the display 1 in related art, however, a flat-panel display such as a plasma display or a liquid crystal display can also realize the system. In the light of a popularization rate of the flat-panel display in recent years, it is presumable that viewing in the liquid crystal display will be the mainstream also in the viewing 3D video contents from now.
As shutters for the shutter glasses, shutters applying liquid crystal shutters are common. The liquid crystal shutters have a structure in which polarizing plates overlap each other on both outer surfaces of glass substrates into which liquid crystal is sealed.
When the user views 3D video by the shutter glasses system, not only 3D video displayed on the display but also objects, landscapes and so on around the display come into sight of the user.
When the user sees objects or landscapes around the display through the liquid crystal shutters, light incident on the liquid crystal shutters (incident light) is non-polarized natural light. At this time, light passing through the liquid crystal shutters will be approximately half (approximately 50%) as much as light before incidence by the polarizing plates in principle, and further, the light will be reduced to approximately 30% due to absorption and dispersion of light by the liquid crystal and the polarizing plates. As described above, due to open and close operations of shutters either of the shutter for the left eye and the shutter for the right eye is inevitably in a closed state, therefore, the light will be further half of approximately 30% as both eyes. That is, light transmittance in the case that the user sees objects or landscapes around the display through the liquid crystal shutters will be approximately 15%.
On the other hand, light emitted from the liquid crystal display (display light) is linear polarized light. Therefore, display light in the case that the user sees 3D video displayed on the liquid crystal display will be linear polarized light. When a polarization axis of the liquid crystal shutters corresponds to the direction of linear polarized light of display light, there is no effect by the polarizing plates described above, therefore, light incident on both eyes of the user will be twice as much as light in the case of the above natural light. That is, light transmittance in the case that the user sees 3D video displayed on the liquid crystal display through the liquid crystal shutters will be approximately 30%.
Therefore, when the polarization axis of the liquid crystal shutters of the shutter glasses corresponds to the direction of linear polarized light of the liquid crystal display, only the display screen of the liquid crystal display is seen bright and the periphery of the display screen of the liquid crystal display is seen dark. As a result, for example, when the user operates a remote controller held in hand, when the user browses a program schedule of a newspaper or when the user turns sideways and has a conversation with a person next to the user during viewing of 3D video, the user feels extremely dark in visual range, therefore, the user may remove the shutter glasses at these situation.
In view of the above, it is proposed stereo glasses in which a rotational portion rotating a filter corresponding to a shutter and a weight portion are provided at a glasses frame (for example, refer to JP-A-10-39254 (Patent Document 1). According to the stereo glasses, the weight portion allows the rotation portion to rotate by inclination of the glasses frame to thereby rotate the filter, as a result, observation is possible without through the filter.